It is well known in the photographic arts to record color images with photographic elements containing dye-providing materials which can be used to provide color images. Although the properties of dyes commonly used to provide such images (e.g. azo or azo-methine dyes) have been optimized over the years, there is a continued search in the art for dyes which provide images having improved stability to heat, light, humidity and chemical reagents.
It is known that dye stability can be enhanced by forming metal-dye complexes. For example, U.S. Pat. No. 4,142,891 (issued Mar. 6, 1979 to Baigrie et al) relates to imaging in diffusion transfer assemblages with metal-complexed azo dyes.
Although metal-dye complexes are favorably regarded for their improved stability, most known metallized dyes or dye precursors are already colored at the time of imagewise exposure. If such dyes and silver halide are incorporated in the same layer of a photographic element, the dye will act as an unwanted filter, absorbing a portion of the incident radiation which otherwise would reach the silver halide. This results in a loss of sensitivity (i.e. photographic speed). Further, such colored dyes or dye precursors cannot be used in conventional white photographic papers.
One way to eliminate the unwanted filtering effect is to have the silver halide and the dye in separate layers while maintaining them in reactive association. While this is a useful and practical solution, it increases the number of layers in the element, making it thicker and presenting manufacturing and imaging inefficiencies.
It would, therefore, be desirable to form highly stable color images using dye precursors which are essentially colorless prior to imagewise exposure and development and can be placed in any layer in the element.